In general, a mobile communication system was developed to provide voice services while guaranteeing activity of users. However, the mobile communication system has gradually expanded its service area up to a data service as well as a voice service, and currently provides a high speed data service. Accordingly, the wireless data traffic demand has continuously increased, and thus a need to support a high data transmission rate has been created.
In general, a method of providing a high data transmission rate includes a method of using a wider frequency band and a method of improving a frequency efficiency. However, in the latter case, it is not easy in reality to further increase the frequency use efficiency through the improvement of technologies since communication technologies of a current generation already provide a frequency use efficiency close to a theoretical limit. Accordingly, a technology using a wide frequency band is spotlighted.
Since a current mobile communication cellular system using a frequency band (<5 GHz) has difficulty in securing a wide frequency band, it is required to secure such a broadband frequency in a higher frequency band. Bands enabling broadband communication at frequencies equal to or higher than 1 GHz are limited by current frequency distribution policy, so that a method using a millimeter wave band equal to or higher than 30 GHz for wireless communication is needed.
However, in such a high frequency band, a problem of seriously generating signal attenuation according to a distance is created. Specifically, propagation path loss increases as a transmission frequency for wireless communication becomes higher, and accordingly, a distance of arrival becomes relatively shorter and a service coverage is reduced. One of main technologies to alleviate the propagation path loss and increase the distance of arrival in order to solve the above problem is a beamforming technique.
Transmit beamforming corresponds to a method of generally concentrating signals transmitted from respective antennas of a plurality of antennas on a particular direction. A type in which a plurality of antennas are arranged may be referred to as an array antenna and an antenna included in the array antenna may be referred to as an element antenna or an antenna element.
Through the use of the transmit beamforming, the distance that the signal can be received, and interference influencing another user is significantly reduced since the signal is almost not transmitted in any direction other than the corresponding direction.
Meanwhile, a receiving side can perform receive beamforming by using a reception array antenna. The receive beamforming corresponds to a technique of concentrating received radio waves on a particular direction to increase the intensity of received signals incident to the corresponding direction, thereby blocking an interference signal.
Such a beamforming technique is advantageous to a communication system of a high frequency band. As a transmission frequency is higher, a wavelength of the radio wave becomes shorter. Accordingly, when antennas are arranged at an interval of half waves, the array antenna can be configured using many more antennas within the same area. That is, the communication system operating at a high frequency band is well positioned to apply the beamforming technique because the communication system can acquire a relatively higher antenna gain in comparison with using the beamforming technique at a low frequency band.